#include <iostream>
using namespace std;

int month_28[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int month_29[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

bool isLeap(int year)
{
    return (year % 400 == 0) || (year % 100 != 0 && year % 4 == 0);
}

int main()
{
    int sum = 0;
    for(int i = 1937; i < 2021; i++)
    {
        if (isLeap(i))
            sum += 366;
        else
            sum += 365;
    }
    sum += 79; //79 = 31 + 28 + 20
    printf("%d", sum / 7);
}